Position detecting method and apparatus

ABSTRACT

A position detecting method including steps of sensing an image of first and second marks, orthogonally transforming a signal obtained in the sensing step, and calculating each position of the first and second marks based on a phase of a corresponding frequency component obtained in the transform step. Patterns are disposed at a first interval in the first mark, patterns are disposed at a second interval in the second mark, and one of the first and second intervals is not an integer multiple of the other of the first and second intervals.

FIELD OF THE INVENTION

This invention relates to a position detecting technique for detecting aposition of a mark.

BACKGROUND OF THE INVENTION

A mark imaging method in an ordinary exposure apparatus formanufacturing semiconductors will be described with reference to FIG. 7.Shown in FIG. 7 are a reticle R, a wafer W that is a substrate to beexposed, a projection optical system 1 in which the optical axis is thez axis, an optical system S for imaging marks that are to be observed,an illumination unit 2 for imaging the marks, a beam splitter 3, opticalsystems 4 and 5 for forming an image, an image sensing unit 6, an A/Dconverter 7, an integrating unit 8, an image processing unit 9, a stagedriving unit 10, a stage 11 that is movable in three dimensions, and aposition measuring unit 12, such as an interferometer, for measuringstage position.

Mark imaging in the exposure apparatus having the above-describedstructure is performed through the following procedure. First, thereticle R is moved by a reticle-stage moving unit (not shown) to aposition at which a reticle mark RM can be observed. Similarly, thestage 11 is moved to a position at which it is possible to observe anobservation mark WM on the wafer W. Initially, the wafer mark WM isilluminated by light flux, which is emitted by the illumination unit 2,via the beam splitter 3, reticle mark RM and projection optical system1. Light flux reflected from the wafer mark WM reaches the beam splitter3 again via the projection optical system 1 and reticle R. The lightflux that has arrived from the projection optical system 1 is reflectedby the beam splitter 3 and forms an image RM of the reticle mark and animage WM of the wafer mark on the image sensing surface of the imagesensing unit 6 via the image forming optical system 5.

FIG. 2A illustrates an example of the observation marks whose imageshave been formed on the image sensing surface in the above description.The reticle mark RM and the wafer mark WM each comprise a plurality ofidentically shaped patterns. The reticle mark and the wafer mark have amark pitch equivalent to a certain fundamental spatial frequency. Theimage sensing unit 6 converts the images of the marks formed on theimage sensing surface into electrical signals (photoelectricconversion). The A/D converter 7 subsequently converts the output of theimage sensing unit 6 to a two-dimensional digital signal sequence.

The integrating unit 8 in FIG. 7 executes integration processing alongthe direction Y of an area WP of the kind shown in FIG. 2A and convertsthe two-dimensional signal to a one-dimensional digital sequence S0(x),as shown in FIG. 2B. On the basis of the digital signal sequence S0(x)obtained by the conversion, the image processing unit 9 uses means, suchas pattern matching or calculation of a center of gravity to measure thecenter positions of the reticle and wafer marks and to measure theirrelative positions.

The above-described method of detecting a mark position is one that isextremely useful in a position detecting apparatus that requiresaccurate detection of the mark position. In the above example of theprior art, however, the signal is a discrete sequence owing to the A/Dconversion for the purpose of processing the electrical signal and,hence, the detected mark positions also are discrete values. Theinfluence of this can no longer be neglected as the need for greaterposition detection accuracy grows.

To deal with this, the specifications of Japanese Patent ApplicationLaid-Open Nos. 3-282715 and 10-284406 disclose techniques for convertingdiscrete sequence signals to signals in a spatial frequency domain by anorthogonal transform and measurement mark position based upon the phaseof a mark-specific spatial frequency component, thereby making itpossible to detect position from discrete sequence signals in a highlyaccurate fashion.

However, in a case wherein the art disclosed in the specifications ofJapanese Patent Application Laid-Open Nos. 3-282715 and 10-284406 isutilized, position must be measured mark by mark in order to measure thepositions of both the reticle mark RM and wafer mark WM. In other words,a processing window must be set separately at the two areas of reticlemark RM and wafer mark WM, and the orthogonal transform, which places aburden on processing, must be performed twice. The problem that arisesis a decline in throughput.

SUMMARY OF THE INVENTION

An object of the present invention is to realize a reduction in time formark position detection that uses an orthogonal transform.

According to one aspect of the present invention, there is provided aposition detecting method comprising steps of sensing an image of firstand second marks, orthogonally transforming a signal obtained in thesensing step, and calculating each position of the first and secondmarks based on a phase of a corresponding frequency component obtainedin the transform step.

Further, according to another aspect of the present invention, there isprovided a position detecting apparatus comprising a sensing unit whichsenses an image of first and second marks, a transform unit whichorthogonally transforms a signal obtained by the sensing unit, and acalculation unit which calculates each position of the first and secondmarks based on a phase of a corresponding frequency component obtainedby the transform unit.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a block diagram for describing the positioning-relatedstructure of an exposure apparatus for manufacturing semiconductorsaccording to a first embodiment of the present invention;

FIGS. 2A and 2B are diagrams illustrating a general example of images ofobservation marks on an image sensing surface and a periodic patternsignal obtained as a result of these observation marks, respectively;

FIGS. 3A and 3B are diagrams illustrating an example of images ofobservation marks on an image sensing surface and a periodic patternsignal obtained as a result of these observation marks, respectively, inthe first embodiment;

FIG. 4 is a diagram illustrating a spatial frequency domain obtained byorthogonally transforming the periodic pattern signal waveform shown inFIG. 3A;

FIG. 5 is a diagram illustrating an example of images of observationmarks on an image sensing surface according to a second embodiment ofthe invention;

FIGS. 6A and 6B are diagrams illustrating an example of images ofobservation marks on an image sensing surface and a periodic patternsignal obtained as a result of these observation marks, respectively, ina third embodiment of the present invention;

FIG. 7 is a block diagram for describing the positioning-relatedstructure of a conventional exposure apparatus for manufacturingsemiconductors;

FIG. 8 is a flowchart for describing the procedure of signal processingaccording to the first embodiment; and

FIG. 9 is a diagram useful in describing the flow of device manufacture.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

First Embodiment

An example in which positioning according to the present invention isapplied to an exposure apparatus for semiconductor manufacture isillustrated below. Shown in FIG. 1 are the reticle R, the wafer W thatis the substrate to be exposed, the projection optical system 1 in whichthe optical axis is the z axis, the optical system S for imaging marksto be observed, the illumination unit 2 for imaging the marks, the beamsplitter 3, the optical systems 4 and 5 for forming an image, the imagesensing unit 6, the A/D converter 7, the integrating unit 8, the imageprocessing unit 9, the stage driving unit 10, the stage 11, which ismovable in three dimensions, the position measuring unit 12, such as aninterferometer, for the position of the stage 11, an orthogonaltransform unit 13, a phase calculation unit 14 and a positioncalculation unit 15. The procedure for mark imaging and positionmeasurement by the positioning arrangement of this embodimentconstructed as set forth above will now be described.

First, the reticle R is moved by a reticle-stage moving unit (not shown)to a position at which the reticle mark RM can be observed. Similarly,the stage 11 is moved to a position at which it is possible to observethe observation mark WM on the wafer W.

Next, light flux for illuminating the observation marks is emitted bythe illumination unit 2. It should be noted that the illumination unit 2may just as well serve as an illumination unit for measuring a focalpoint. The light flux emitted from illumination unit 2 illuminates thewafer mark WM via the beam splitter 3, reticle mark RM and projectionoptical system 1. Light flux reflected from the wafer mark WM reachesthe beam splitter 3 again via the projection optical system 1 andreticle R. The light flux that has arrived is reflected by the beamsplitter 3 and forms the image RM of the reticle mark and the image WMof the wafer mark on the image sensing surface of the image sensing unit6 via the image forming optical system 5.

FIG. 3A illustrates an example of images of the observation marks on theimage sensing surface. The reticle mark RM and the wafer mark WM eachcomprise a plurality of identically shaped patterns. In FIG. 3A, theimage of wafer mark WM is arranged to fall between the images of reticlemarks RM, though an arrangement in which the reticle mark RM fallsbetween the wafer marks WM may be adopted. However, it should be notedthat the image of the reticle mark RM is disposed on the image sensingsurface with a line width and pitch that differ from those of the wafermarks WM on the image sensing surface. Pitch PR of the reticle mark andpitch PW of the wafer mark are related by the equation PW≠mPR (where mis an arbitrary integer). Further, in a case wherein processing isexecuted upon inserting the wafer mark WM between the reticle marks, asshown in FIG. 3A, a span SR of the reticle marks RM bracketing the wafermark WM is expressed by the equation SR=nSR (where n is an arbitraryinteger). (It should be noted that in a case wherein a mark is notinserted between marks, positioning is performed in such a manner thatthe mark positions obtained will be spaced apart a prescribed distancerather than be made to coincide.)

The group of marks described above is imaged and subjected tophotoelectric conversion by the image sensing unit 6. The A/D converter7 subsequently converts the output of the image sensing unit 6 to atwo-dimensional digital signal sequence. The integrating unit 8 in FIG.1 executes integration processing along the direction Y of the area WPof the kind shown in FIG. 3A and converts the two-dimensional signal toa one-dimensional digital signal sequence S0(x), as shown in FIG. 3B.The mark positions are then calculated by processing the digital signalsequence, which has been obtained by the conversion, by the method setforth in the specifications of Japanese Patent Application Laid-OpenNos. 3-282715 and 10-284406.

A case wherein the mark-position calculation method disclosed in thespecification of Japanese Patent Application Laid-Open No. 10-284406 isapplied will now be described.

FIG. 8 is a flowchart for describing the procedure of signal processingaccording to this embodiment. In FIG. 8, a periodic pattern is generatedat step S1. More specifically, a one-dimensional discrete signalsequence having a periodicity of the kind shown in FIG. 3B is generatedby the integrating unit 8 and supplied to the orthogonal transform unit13.

Next, at step S2, the orthogonal transform unit 13 applies orthogonaltransform processing to the signal that enters from the integrating unit8. Here, a well-known orthogonal transform, such as a discrete Fouriertransform is applied to the input signal to convert the signal to aspatial frequency domain. For example, in a case wherein a discreteFourier transform is used as the orthogonal transform, values in thespatial frequency domain can be obtained by the following transformationformulae:

$\begin{matrix}{{{Xr}(f)} = {\sum\limits_{n = {{- N}/2}}^{n = {N/2}}{{x\left( {{xo} + n} \right)}{\cos\left( {{- 2}\pi\;{{nf}/N}} \right)}}}} & (1) \\{{{Xi}(f)} = {\sum\limits_{n = {{- N}/2}}^{n = {N/2}}{{x\left( {{xo} + n} \right)}{\sin\left( {{- 2}\pi\;{{nf}/N}} \right)}}}} & (2)\end{matrix}$

In Equations (1) and (2) above, x represents an input signal sequence,Xr the real-number part of a spatial frequency component, Xi theimaginary-part of a spatial frequency component, N the processing widthof the discrete Fourier transform, xo a position at which phase isdetected at the center of the processing range of the discrete Fouriertransform, and f a frequency of interest, which is the frequency of thespatial frequency component sought.

In the orthogonal transform, the values at all frequencies are obtainedand the frequency for which power is maximized is selected. FIG. 4illustrates the spectrum distribution after the application of theorthogonal transform. Since the pitch of the reticle mark RM and that ofthe wafer mark WM differ, the distribution has peaks at spatialfrequencies fR, fW that differ from each other. The phases of thespatial frequencies fR, fW corresponding to the peaks are obtained bythe phase calculation unit 14 at a step S3 and the mark positions arecalculated by the position calculation unit 15 at step S4.

First, the phase calculation unit 14 uses the following well-knownEquation (3) to calculate the phase θ of a spatial frequency componentfor which a pattern to be detected in the spatial frequency domainappears uniquely:

$\begin{matrix}{\theta = {{arc}\;{{\tan\left( \frac{{Xi}(f)}{{Xr}(f)} \right)}.}}} & (3)\end{matrix}$

Here, the phase θ is obtained with regard to a case wherein f is fR withregard to a case wherein f is fW.

Next, the position calculation unit 15 uses Equation (4) below tocalculate mark position d from the phase θ obtained by the phasecalculation unit 14. It should be noted that the two mark positions,namely, the reticle mark position and wafer mark position, arecalculated in association with the two phases obtained by the phasecalculation unit 14.

$\begin{matrix}{d = {{xo} + \left( \frac{\theta\; N}{\pi\; f} \right)}} & (4)\end{matrix}$

This equation is the result of adding the amount of phase advanceobtained when the periodic pattern signal advances by the amount of thephase θ to xo. Accordingly, the relative positions between the twomarks, namely, the reticle mark RM and the wafer mark WM, can bedetected and the positioning of the reticle and wafer can be carriedbased upon the results of the detection.

Thus, in accordance with the first embodiment as described above, thereticle mark RM and the wafer mark WM are disposed at mutually differentline widths and pitches, it is so arranged that the pitch PR of thereticle mark and pitch PW of the wafer mark will satisfy the inequalityPW≠mPR (where m is an arbitrary integer), and the discrete sequencesignal is orthogonally transformed, whereby the fundamental spatialfrequency component of each mark can be obtained by executing orthogonaltransform processing a single time and the position of each mark can befound accurately from the phase of the fundamental spatial frequencycomponent corresponding to each mark. In other words, the relativepositions of the reticle mark RM and the wafer mark WM can be obtainedby executing orthogonal transform processing a single time. As a result,highly precise detection of position is possible and the problemrelating to throughput does not arise.

Further, in accordance with the above-described technique, mark positionis detected by taking note of the periodicity of the signal sequence. Asa result, there is little susceptibility to effects of noise that may becontained in the signal.

Signal Embodiment

A second embodiment relating to positioning of a wafer and a reticle inan exposure apparatus for semiconductor manufacture is illustratedbelow. In the first embodiment, position is detected from marks arrayedin one dimension and, therefore, position can only be calculated in onedirection from one mark. In the second embodiment, it is so arrangedthat position detecting corresponding to two directions can be performedusing a single mark. It should be noted that the structure of theapparatus relating to positioning is similar to that of the firstembodiment (see FIG. 1) and need not be illustrated and described again.

FIG. 5 is a diagram illustrating an example of observation marks whoseimages are formed on the image sensing surface of the image sensing unit6. The marks employed in the second embodiment are obtained by disposingreticle mark RM composed of a plurality of identically shaped patternsand reticle mark WM composed of a plurality of identically shapedpatterns. Furthermore, identically shaped marks are disposed in twomutually orthogonal directions in such a manner that measurement alongthe x, y directions can be performed from an image obtained by a singleimage sensing operation.

As shown in FIG. 5, the images of the reticle mark RM and the wafer markWM are disposed on the image sensing surface at mutually different linewidths and pitches, and it is so arranged that the pitch PR of thereticle mark and pitch PW of the wafer mark are related by the equationPW≠mPR (where m is an arbitrary integer). Further, it is so arrangedthat the span SR of the reticle marks RM is expressed by the equationSR=n₁PR (where n₁ is an arbitrary integer), and it is so arranged thatspan SW of the wafer marks WM is expressed by the equation SW=n₂PW(where n₂ is an arbitrary integer). Even though the images of the marksthus disposed on the image sensing surface are spaced apart by therespective spans SR, SW, there is no influence upon the orthogonaltransform because the phases are equal, and measurement of the markpositions can be performed through a method similar to that described inthe first embodiment.

Third Embodiment

A third embodiment relating to positioning of a wafer and an article inan exposure apparatus for semiconductor manufacture is illustratedbelow. A very high precision is required for aligning a wafer and areticle, and it is required that the positions of the wafer mark andreticle mark be found in a highly accurate fashion. Accordingly, in thethird embodiment, at least one of the wafer mark and the reticle markhas mark pitches exhibiting different fundamental spatial frequencies,and the position of each mark is detected with high precision byapplying the position detection method described in the first and secondembodiments. More specifically, in the first and second embodiments, thepositions of the reticle mark and wafer mark are obtained and theirrelative positions are calculated. In the third embodiment, however, amark of a different fundamental spatial frequency is provided in onemark (e.g., the reticle mark) and it is so arranged that calculation ofcoarse and fine positions can be calculated by applying an orthogonaltransform a single time. It should be noted that structure of theapparatus relating to positioning is similar to that of the firstembodiment (see FIG. 1) and need not be illustrated or described again.

FIGS. 6A and 6B are diagrams illustrating an example of observationmarks whose images are formed on the image sensing surface of the imagesensing unit 6 in the third embodiment. An observation mark (wafer mark)according to the third embodiment is composed of a plurality ofidentically shaped patterns. As shown in FIG. 6A, the image of wafermark WM1 is disposed on the image sensing surface with a line width andpitch that differ from those of a wafer mark WM2 on the image sensingsurface. It is so arranged that pitch PW1 and pitch PW2 of the wafermarks are related by the equation PW1≠mPW2 (where m is an arbitraryinteger). If calculation of mark position is performed by a methodsimilar to that of the first embodiment using such marks, xo is decidedupon by obtaining the coarse position of the wafer mark at WM1 havingthe coarse pitch, then, the position of WM2 having the finer pitch iscalculated and xo is corrected, whereby a more accurate mark positioncan be obtained.

The third embodiment has been described with regard to a wafer mark.However, similar processing may be executed by disposing marks having adifferent mark pitch of the above kind also on the reticle side.

In each of the above embodiments, it is also possible to utilize aperiodic pattern included in actual elements (actual circuit patterns)as a periodic pattern composed of a group of marks.

The main characterizing features relating to each of the foregoingembodiments may be summarized as follows:

In a mechanism that performs position detection based upon alignmentmarks comprising a plurality of repeating patterns, first, a signalwaveform conforming to the repetition of the plurality of patterns ofthe alignment marks (FIGS. 3A, 3B and FIGS. 6A, 6B) is generated (imagesensing unit 6, A/D converter 7 and integrating unit 8). The signalwaveform generated is subjected to an orthogonal transform by theorthogonal transform unit 13 to generate a spatial frequency domainsignal, and a plurality of peaks corresponding to different fundamentalspatial frequencies are detected based upon peak positions in a (power)spectrum signal according to the spatial frequency domain signal (fW,fR, FIG. 4). The phase calculation unit 14 then obtains the phasesregarding the fundamental spatial frequency component corresponding toeach of the plurality of peaks detected, and the position calculationunit 15 calculates pattern position based upon the phases obtained.

In particular, with regard to generation of the signal waveform in theimage sensing unit 6, A/D converter 7 and integrating unit 8, in thefirst and second embodiments, there is generated a signal waveform (FIG.3A) that corresponds to alignment marks obtained by observing analignment mark (RM), which is provided on the surface of a first object,and an alignment mark (WM), which is provided on the surface of a secondobject, in such a manner that these alignment marks combine. Theposition of the alignment mark provided on the surface of the firstobject and the position of the alignment mark provided on the surface ofthe second object are calculated by orthogonal transform unit 13, phasecalculation unit 14 and position calculation unit 15.

It should be noted that, it is preferred that the different fundamentalspatial frequencies differ from each other by an integral multiple.

Further, in the third embodiment, a coarse position of an alignment markis obtained based upon a phase calculated with regard to a lowfundamental frequency (WM1 in FIG. 6), and a fine position is calculatedupon correcting the coarse position based upon a phase calculated withregard to a higher basic fundamental frequency (WM2 in FIG. 6A).

Further, in the first and second embodiments, there are supplied a firstsubstrate (reticle R) having an alignment mark (RM) comprising aplurality of patterns that repeat at intervals PR, and a secondsubstrate (wafer W) having an alignment mark (WM) comprising a pluralityof patterns that repeat at intervals PW, where PR≠mPW holds (and m is aninteger). A signal corresponding to the row of the plurality of patterns(FIG. 3B) is generated from combined alignment marks (FIG. 3A, FIG. 5)obtained by simultaneously observing the alignment marks on the firstand second substrates. The generated signal is subjected to anorthogonal transform in the orthogonal transform unit 13 to obtain aspatial frequency domain signal. Two peaks (fW, fR) corresponding to thefundamental frequencies conforming to the intervals PR and PW aredetected based upon peak position in this spatial frequency domainsignal. The phase calculation unit 14 then obtains the phases regardingthe fundamental spatial frequencies corresponding to the two peaksdetected, and the position calculation unit 15 calculates the positionsof the positioning patterns on the first and second substrates basedupon the phases obtained.

Further, in accordance with the first embodiment, the alignment mark onthe first substrate has a portion in which patterns disposed over aninterval SR=nPR (where n is an integer) is located in a row of thepatterns that repeat at the intervals PR, and the combined alignmentmarks (FIG. 3A) are such that a plurality of patterns on the secondsubstrate are disposed between the patterns space apart by the intervalSR.

Further, in accordance with the second embodiment, the alignment mark onthe first substrate has a portion in which patterns are disposed over aninterval SR=nPR (where n is an integer), and two of these alignmentmarks are provided (FIG. 5) so as to intersect orthogonally in theportion of interval SR. The alignment mark on the second substrate has aportion in which patterns are disposed over an interval SW=kPW (where kis an integer), and two of these alignment marks are provided (FIG. 5)so as to intersect orthogonally in the portion of interval SW. Thecombined alignment marks are such that the alignment mark on the secondsubstrate is disposed in a space formed by the portion having theinterval SR of the alignment mark on the first substrate (FIG. 5).

A process for manufacturing a semiconductor device, such as amicrodevice utilizing the exposure apparatus set forth above, will nowbe described.

FIG. 9 is a diagram illustrating the overall flow of a process ofmanufacturing the semiconductor device. The circuit for thesemiconductor device is designed at step S1 (circuit design). A mask isfabricated at step S2 (mask fabrication) based upon the circuit patterndesigned.

Meanwhile, a wafer is manufactured using a material such as silicon atstep S3 (wafer manufacture). Using the above-described mask and wafer,the above-described exposure apparatus forms the actual circuit on thewafer utilizing lithography at step S4 (wafer process), which is alsoreferred to as “pre-treatment”. A semiconductor chip is obtained, usingthe wafer fabricated at step S4, at step S5 (assembly), which is alsoreferred to as “post-treatment”. This step includes steps such asassembly (dicing and bonding) and packaging (chip encapsulation). Thesemiconductor device fabricated at step S5 is subjected to inspectionssuch as an operation verification test and a durability test at step S6(inspection). The semiconductor device is completed through these stepsand then is shipped at step S7.

The wafer process of step 4 above has the following steps including anoxidizing step of oxidizing the surface of the wafer, a CVD step offorming an insulating film on the wafer surface, an electrode formingstep of electrodes on the wafer by vapor deposition, an ion implantationstep of implanting ions in the wafer, a resist treatment step of coatingthe wafer with a photoresist, an exposure step of transferring thecircuit pattern to the wafer by the above-described exposure apparatusafter the resist treatment step, a developing step of developing thewafer exposed at the exposure step, an etching step of etching awayportions other than the photoresist developed at the developing step,and a resist removing step of removing unnecessary resist left afteretching is performed. Multiple circuit patterns are formed on the waferby implementing these steps repeatedly.

In accordance with the present invention, as described above, it ispossible to raise the speed mark position detection that uses anorthogonal transform.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

CLAIM OF PRIORITY

This application claims priority from Japanese Patent Application No.2003-029674 filed on Feb. 6, 2003, which is hereby incorporated byreference herein.

1. A position detecting method comprising steps of: sensing an image offirst and second marks; orthogonally transforming a signal obtained insaid sensing step; and calculating each position of the first and secondmarks based on a phase of a corresponding frequency component obtainedin said transforming step, wherein patterns are disposed at a firstinterval in the first mark, patterns are disposed at a second intervalin the second mark, and one of the first and second intervals is not aninteger multiple of the other of the first and second intervals.
 2. Aposition detecting method comprising steps of: sensing an image of firstand second marks; orthogonally transforming a signal obtained in saidsensing step; and calculating each position of the first and secondmarks based on a phase of a corresponding frequency component obtainedin said transforming step, wherein the first mark includes two groups ofpatterns, in each of the two groups patterns are disposed at an intervalA, the two groups are disposed at an interval nA, where n is an integer,and the second mark falls within the interval nA in the signal.
 3. Aposition detecting apparatus comprising: a sensing unit which senses animage of first and second marks; a transform unit which orthogonallytransforms a signal obtained by said sensing unit; and a calculationunit which calculates each position of the first and second marks basedon a phase of a corresponding frequency component obtained by saidtransform unit, wherein patterns are disposed at a first interval in thefirst mark, patterns are disposed at a second interval in the secondmark, and one of the first and second intervals is not an integermultiple of the other of the first and second intervals.
 4. An exposureapparatus for exposing a substrate to a pattern, said apparatuscomprising: a position detecting apparatus as defined in claim
 3. 5. Adevice manufacturing method comprising: a step of exposing a substrateto a pattern using an exposure apparatus as defined in claim
 4. 6. Aposition detecting apparatus comprising: a sensing unit which senses animage of first and second marks; a transform unit which orthogonallytransforms a signal obtained by said sensing unit; and a calculationunit which calculates each position of the first and second marks basedon a phase of a corresponding frequency component obtained by saidtransform unit, wherein the first mark includes two groups of patterns,in each of the two groups patterns are disposed at an interval A, thetwo groups are disposed at an interval nA, where n is an integer, andthe second mark falls within the interval nA in the signal.
 7. Anexposure apparatus for exposing a substrate to a pattern, said apparatuscomprising: a position detecting apparatus as defined in claim
 6. 8. Adevice manufacturing method comprising: a step of exposing a substrateto a pattern using an exposure apparatus as defined in claim 7.